namei: don't mangle nd->seq in lookup_fast()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index 97315df..e321450 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1134,7 +1134,7 @@ static inline int managed_dentry_rcu(struct dentry *dentry)
  * we meet a managed dentry that would need blocking.
  */
 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
-                              struct inode **inode)
+                              struct inode **inode, unsigned *seqp)
 {
        for (;;) {
                struct mount *mounted;
@@ -1161,7 +1161,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
                path->mnt = &mounted->mnt;
                path->dentry = mounted->mnt.mnt_root;
                nd->flags |= LOOKUP_JUMPED;
-               nd->seq = read_seqcount_begin(&path->dentry->d_seq);
+               *seqp = read_seqcount_begin(&path->dentry->d_seq);
                /*
                 * Update the inode too. We don't need to re-check the
                 * dentry sequence number here after this d_inode read,
@@ -1397,7 +1397,8 @@ static struct dentry *__lookup_hash(struct qstr *name,
  *  It _is_ time-critical.
  */
 static int lookup_fast(struct nameidata *nd,
-                      struct path *path, struct inode **inode)
+                      struct path *path, struct inode **inode,
+                      unsigned *seqp)
 {
        struct vfsmount *mnt = nd->path.mnt;
        struct dentry *dentry, *parent = nd->path.dentry;
@@ -1437,8 +1438,8 @@ static int lookup_fast(struct nameidata *nd,
                 */
                if (__read_seqcount_retry(&parent->d_seq, nd->seq))
                        return -ECHILD;
-               nd->seq = seq;
 
+               *seqp = seq;
                if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
                        status = d_revalidate(dentry, nd->flags);
                        if (unlikely(status <= 0)) {
@@ -1449,10 +1450,10 @@ static int lookup_fast(struct nameidata *nd,
                }
                path->mnt = mnt;
                path->dentry = dentry;
-               if (likely(__follow_mount_rcu(nd, path, inode)))
+               if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
                        return 0;
 unlazy:
-               if (unlazy_walk(nd, dentry, nd->seq))
+               if (unlazy_walk(nd, dentry, seq))
                        return -ECHILD;
        } else {
                dentry = __d_lookup(parent, &nd->last);
@@ -1543,7 +1544,7 @@ static void terminate_walk(struct nameidata *nd)
                put_link(nd);
 }
 
-static int pick_link(struct nameidata *nd, struct path *link)
+static int pick_link(struct nameidata *nd, struct path *link, unsigned seq)
 {
        int error;
        struct saved *last;
@@ -1553,7 +1554,7 @@ static int pick_link(struct nameidata *nd, struct path *link)
        }
        if (nd->flags & LOOKUP_RCU) {
                if (unlikely(nd->path.mnt != link->mnt ||
-                            unlazy_walk(nd, link->dentry, nd->seq))) {
+                            unlazy_walk(nd, link->dentry, seq))) {
                        return -ECHILD;
                }
        }
@@ -1577,13 +1578,14 @@ static int pick_link(struct nameidata *nd, struct path *link)
  * so we keep a cache of "no, this doesn't need follow_link"
  * for the common case.
  */
-static inline int should_follow_link(struct nameidata *nd, struct path *link, int follow)
+static inline int should_follow_link(struct nameidata *nd, struct path *link,
+                                    int follow, unsigned seq)
 {
        if (likely(!d_is_symlink(link->dentry)))
                return 0;
        if (!follow)
                return 0;
-       return pick_link(nd, link);
+       return pick_link(nd, link, seq);
 }
 
 enum {WALK_GET = 1, WALK_PUT = 2};
@@ -1592,6 +1594,7 @@ static int walk_component(struct nameidata *nd, int flags)
 {
        struct path path;
        struct inode *inode;
+       unsigned seq;
        int err;
        /*
         * "." and ".." are special - ".." especially so because it has
@@ -1604,7 +1607,7 @@ static int walk_component(struct nameidata *nd, int flags)
                        put_link(nd);
                return err;
        }
-       err = lookup_fast(nd, &path, &inode);
+       err = lookup_fast(nd, &path, &inode, &seq);
        if (unlikely(err)) {
                if (err < 0)
                        return err;
@@ -1614,6 +1617,7 @@ static int walk_component(struct nameidata *nd, int flags)
                        return err;
 
                inode = path.dentry->d_inode;
+               seq = 0;        /* we are already out of RCU mode */
                err = -ENOENT;
                if (d_is_negative(path.dentry))
                        goto out_path_put;
@@ -1621,11 +1625,12 @@ static int walk_component(struct nameidata *nd, int flags)
 
        if (flags & WALK_PUT)
                put_link(nd);
-       err = should_follow_link(nd, &path, flags & WALK_GET);
+       err = should_follow_link(nd, &path, flags & WALK_GET, seq);
        if (unlikely(err))
                return err;
        path_to_nameidata(&path, nd);
        nd->inode = inode;
+       nd->seq = seq;
        return 0;
 
 out_path_put:
@@ -2342,7 +2347,7 @@ done:
                put_link(nd);
        path->dentry = dentry;
        path->mnt = nd->path.mnt;
-       error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW);
+       error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW, 0);
        if (unlikely(error))
                return error;
        mntget(path->mnt);
@@ -2939,6 +2944,7 @@ static int do_last(struct nameidata *nd,
        bool will_truncate = (open_flag & O_TRUNC) != 0;
        bool got_write = false;
        int acc_mode = op->acc_mode;
+       unsigned seq;
        struct inode *inode;
        struct path save_parent = { .dentry = NULL, .mnt = NULL };
        struct path path;
@@ -2959,7 +2965,7 @@ static int do_last(struct nameidata *nd,
                if (nd->last.name[nd->last.len])
                        nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
                /* we _can_ be in RCU mode here */
-               error = lookup_fast(nd, &path, &inode);
+               error = lookup_fast(nd, &path, &inode, &seq);
                if (likely(!error))
                        goto finish_lookup;
 
@@ -3047,6 +3053,7 @@ retry_lookup:
 
        BUG_ON(nd->flags & LOOKUP_RCU);
        inode = path.dentry->d_inode;
+       seq = 0;        /* out of RCU mode, so the value doesn't matter */
        if (unlikely(d_is_negative(path.dentry))) {
                path_to_nameidata(&path, nd);
                return -ENOENT;
@@ -3054,7 +3061,7 @@ retry_lookup:
 finish_lookup:
        if (nd->depth)
                put_link(nd);
-       error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW);
+       error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW, seq);
        if (unlikely(error))
                return error;
 
@@ -3072,6 +3079,7 @@ finish_lookup:
 
        }
        nd->inode = inode;
+       nd->seq = seq;
        /* Why this, you ask?  _Now_ we might have grown LOOKUP_JUMPED... */
 finish_open:
        error = complete_walk(nd);